There are no official pics of the new Slide Pad add-on yet, but it works like a cradle into which you fit the 3DS, a bit like a more streamlined version of the recharge cradle. The Slide Pad then gives you three extra shoulder buttons (R1, R2, and L2 - L1 on the console is kept the same), an earphone socket and, most importantly, a second Circle Pad.

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The news was revealed in Japanese games mag Famitsu, which shows the new Circle Pad sitting to the right of the face buttons and looking just slightly smaller than the existing one on the console.

There's no price yet for the Slide Pad but it's believed to be around $10. It'll almost certainly be bundled with several games too. The news is exactly as predicted by French website 01net, who originally predicted many of the details of the Wii U.
Announced at the same time as the Circle Pad is a version of Wii game Monster Hunter Tri. Although Monster Hunter is a niche franchise at best in the West, in Japan it's one of the most successful ever and almost the sole reason the PSP originally thrived in the country.

According to website Andriasang Monster Hunter 3G will be an 'expanded version' of the original game and will feature local wireless play, but there's no mention of an online option (many of the Monster Hunter games don't feature online play, as meeting up socially to play it is one of its main appeals in Japan).
The game's going to be playable at the Tokyo Game Show and since we'll be there we'll try and push through the crowds and give a report back. The only specified new features so far are a quick turn control option on the touchscreen and improved controls while under water.

The news virtually guarantees that Nintendo's planned press conference on the 13th September, which is already known to be about a 'new product line' for the 3DS, is a new version of the console with the extra Circle Pad and shoulder buttons built in.